The field of the invention is headphones, and more particularly, high fidelity headphones for reproducing quadraphonically recorded program material.
As indicated in copending U.S. Pat. No. 3,924,072 issued on Dec. 2, 1975 and entitled "Headphone With Ambience Control", commercially available recordings include separate channels of program information which are formed by combining signals from microphones disposed throughout the recording studio. Stereophonic recordings are formed by combining these signals into two channels and quadraphonic recordings are formed by combining them into four channels. When reproduced by loudspeakers, recorded quadraphonic program material reaches both ears of the listener to not only provide directionally, but also to provide a natural mixing of the channels. This mixing is not merely the addition of a portion of one channel to the others, but is instead, a complex addition of phase shifted sounds which varies depending upon the position of the listener in the room, the orientation of his head, the frequency of the program material and size, shape and contents of the room.
Such mixing does not occur when the recorded program material is reproduced through headphones. The program material is instead coupled directly to the left or right ear of the listener, and as a result, apparent gaps between discrete sound sources may occur rather than a continuous "panorama" of sound. In the above cited patent, a means for overcoming this effect in stereophonic headphones is disclosed in which a portion of the signal from each channel is electrically phase shifted and applied to the transducer of the other channel.
There are a number of commercially available quadraphonic headphones, all of which include four audio transducers that are each connected to receive one of the four quadraphonic channels. Two of the transducers are mounted in each headphone cup, with the left front and left back channels being applied directly to the listener's left ear and the right front and right back channels being applied to his right ear. Typically, no mixing occurs between the left and right channels, whereas nearly total mixing occurs between the front and back channels on each side. The resulting effect is substantially different from that obtained by listening to the same quadraphonic program material through a loudspeaker system where "natural" mixing of the four channels ocurs before reaching the ears of the listener.